Yes, I have experienced job insecurity in that I wait until the middle of my current semester to find out if I will have employment the following semester. Until that point, and until I am actually in front of the class, I am not certain I will be employed. This is nerve racking as if I do not receive an offer I will have to furiously seek employment elsewhere in a very short period of time.
I have had classes cancelled and changed at the last minute. This has worked to my advantage in some instances, another class section offering or a better time, and to my disadvantage in other instances, a complete class cancellation, without a replacement or alternate employment scheduled, at the last minute.
If I do not receive an offer, I will most certainly return to school.